This invention relates generally to cable television systems and electronic devices used in such systems, and more specifically fuses included in electronic devices.
A communication system 100, such as a two-way cable television system, is depicted in FIG. 1. The communication system 100 includes headend equipment 105 for generating forward signals that are transmitted in the forward, or downstream, direction along a communication medium, such as a fiber optic cable 110, to an optical node 115 that converts optical signals to radio frequency (RF) signals. The RF signals are further transmitted along another communication medium, such as coaxial cable 120, and are amplified, as necessary, by one or more distribution amplifiers 125 positioned along the communication medium. Taps 130 included in the cable television system split off portions of the forward signals for provision to subscriber equipment 135, such as set top terminals, computers, and televisions. In a two-way system, the subscriber equipment 135 can also generate reverse signals that are transmitted upstream, amplified by any distribution amplifiers 125, converted to optical signals, and provided to the headend equipment 105.
Network powering devices, such as power supplies, are typically included in many of the devices of the communication system 100 or as separate devices located along the communication medium, such as coaxial cable. The power supplies usually generate both 60 volts alternating current (VAC) and 90VAC power and supply 6 amperes (A) to 15A of current to the powered devices, for example, optical nodes or amplifiers. Power supplies are typically located throughout the communication system 100 near the center of a pocket of amplifiers to maximize the power efficiency. AC power from the power supply enters a power inserter installed on the coaxial cable and combines the AC power with the RF signals. The power inserter then directs the power in both directions along the coaxial cable.
One problem that occurs with some regularity in a communication system 100 is a service outage due to powering faults. Typically, a powering fault may be caused by voltage and current surges or lightning strikes that affect the surrounding devices on the coaxial cable. As a result, there is an increased expectation that devices along the communication medium be designed to adequately prevent service outages, or at the least, protect the devices along the communication medium from failure when powering faults occur within the communication system 100.
Thus, what is needed is a protective device for use in communication devices, such as distribution amplifiers, to provide improved reliability and surge-resistance. Due to development time and the cost of installing new equipment, however, it is also important that a protective device retrofit easily and inexpensively into existing products to keep upgrade costs to a minimum.